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It depends a lot on what you want to see. I imagine your dobsonian has a primary focal length around 1500mm
Under good conditions the best magnification you can expect will be about 300x. using a 5mm eypiece or a 10mm with a x2 Barlow. Barlows and short focal length eyepieces in theory can give higher magnification but generally about 100x will be all you can use except on very bright objects such as moon craters.
A good Barlow on a 25mm Plossl will probably give a clearer view than a poor 10 mm plossl.
If the 10mm lens gives a fuzzy view bare it is doubtful if a Barlow will do more than make a fuzzy image larger.
However seeing conditions are the main criteria for the use of high magnification and top quality eyepieces will give better views than mediocre eyepieces and a Barlow.
Barry
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